Data communication has been with us for a long time. Smoke signals, drum beats, horn and bugle calls, and the telegraph, are all traditional examples of communication systems. More contemporary systems include the conventional telephone, and more recently, the computer network. The effectiveness of any traditional or contemporary system to communicate information is related to the particular system's ability to overcome two obstacles, namely, interference and noise.
Interference occurs when a desired signal and one or more unwanted signals are received at or near the same time. Interference causes the desired signal to be incorrectly received due to the reception of the unwanted signal. For example, assume that A and B are communicating with one another by beating their respective drums. While A and B communicate, C begins beating its drum. C's signals are received by A and B causing their communication to be partially, or even completely, meaningless. C's signal is said to interfere with the communication between A and B. Interference therefore is the presence of at least one unwanted communication signal which interferes with the reception of a desired communication signal.
Noise, on the other hand, is another disturbance introduced into a communication system which is not an interfering signal. Noise may partially, or completely, distort or garble the information content of the desired signal. To continue with the above example, assume that while A and B are communicating, a freight train passes between them. The noise from the freight train at least partially disturbs A's and B's communication. Noise therefore is any disturbance that affects a desired communication signal and is not an interfering signal. The static received during a telephone call is another example of noise.
Contemporary computer network and telephone systems have traditionally been "wired" communication systems. In other words, each computer or telephone is physically joined with one or more other computers or telephones using a wire, fiber optic cable, or another suitable communication medium. Each computer, group of related computers, or telephony system is referred to as a node within these communication systems. A node is a junction point within a communication system.
Wireless communication between the nodes of communication systems is becoming increasingly widespread. As a result of this increased ubiquity, an ever increasing number of people are communicating using wireless signals, and thereby increasing the potential for interference. In cellular telephony systems for example, it is common for two people located relatively close to one another, and who are involved in two separate conversations, to interfere with one another's communication signal.
Conventional attempts to solve this problem include without limitation, modeling interference as noise and using error control coding to mitigate the effects, implementing systems with multiple antennas, and using power control to limit the effect of spatially distant nodes utilizing the same transmission frequency. These solutions however fail to address the fundamental issue, namely that interference is caused by another user, in turn causing less than optimal decoding of received signals. This results in performance degradation. The inability of conventional solutions to substantially eliminate the effects of interference and noise remain a dominant obstacle to producing cost-effective and more commercially successful products.